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Researchers Note Cautions About Geron Drug

This morning, an abstract containing new data on GeronGeron’s drug imetelstat caused shares in the tiny, Menlo Park, Calif., biotechnology company to more than double to $7.78; they fell some, but still ended the day up 44% to $5.20, giving Geron a market capitalization of $670 million. Obviously, excitement around this medicine is high.

Here’s the reason: the data seem to suggest that imetelstat might reverse the effects of myelofibrosis, a type of cancer that turns the bone marrow into scar tissue. That’s something IncyteIncyte’s Jakafi, a newly approved treatment, does not do, nor do other, similar drugs known as JAK inhibitors. That would represent real hope for these patients.

I asked two top experts in the field, Gary Gilliland, the former head of cancer research at MerckMerck and the Vice President for Precision Medicine at Penn Medicine, and Alan List, the President and CEO of Moffitt Cancer Center, for their thoughts on the data.

“It’s very interesting data but it’s very early, they have small numbers of patients with modest follow up,” says Gilliland. “I hate the hype that comes out around this because these patients are so desperate for treatments.”

In the exciting column: Four of 18 patients had blood test results consistent with a complete remission of disease, and one more with a partial remission and three with clinical improvement.

Gilliland says he’d want to know more about how sick they were at the beginning of the study – healthier patients are more likely to look like they’ve gone into remission based on a blood test. Myelofibrosis can be spotty, he says, so it’s useful to have long-term biopsies to make sure the bone marrow is improving. “Three months is different from two years.”

List notes that a blood test result is not enough to judge a complete remission. “These are not true CRs,” he says. But he’s encouraged by the fact that there was reversal of fibrosis, the bone marrow scarring, in the four patients whose blood tests showed signs of the cancer disappearing. “At least it’s evidence of activity,” he says. “The JAK inhibitors have no effect on fibrosis at all.”

But List does see a “major problem” for the Geron drug. Even for high-risk myelofibrosis patients, the condition is chronic. Imetelstat is likely to be given intravenously once a week for three weeks, followed by once every three weeks. With that dosing schedule, it’s going to be very difficult to get patients to stick to the regimen. “If you can get to a more extended schedule it makes a lot more sense,” List says.

Imetelstat is a new type of drug that blocks telomerase, an enzyme that adds protective ends of extra DNA to the ends of chromosomes. Cancer cells use telomerase to extend their lives and continue to multiply, and it’s been considered a promising target for anti-cancer medicines for many years, but if the drug reaches the market it would be the first of its kind.

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All patients had intermediate 2 or High risk. Patients had Primary MF, Post decentral essential thrombocythemia MF, and post PV MF. There is no treatment that has ever generated GRs in these populations.

With all the caveats that go along with reasoning from first principles, I think that it might be worth pointing out that Imetelstat is structurally related to antisense drugs. The latter compounds have shown very little activity in leukemia and other diseases of the bone marrow, apparently because they carry a large number of negative charges and do not enter cells very efficiently.